1. Field of the Invention
The present invention relates to a heat exchanger for use in air-conditioners such as automotive air-conditioners, package air-conditioners and room air-conditioners.
2. Description of the Prior Art
In general, a heat exchanger for an air-conditioner is composed, in combination, of a number of fins and a plurality of heat transfer tubes held in contact with the fins. A severed, raised louver structure is formed on a surface of each fin in order to effectively carry out heat exchange between coolant that flows within the heat transfer tubes and air that flows between the fins in contact with the fin surfaces. U.S. Pat. No. 3,438,433 shows a heat exchanger of this type. However, if the louvers are arranged as proposed in that U.S. patent, a temperature boundary layer formed on the louvers would grow without any separation, so that a heat transfer performance of the louvers on the downstream side is degraded. In particular, in the case where the width of the louvers is small, the performance of the heat exchanger will be considerably degraded degrade. Thus, the heat exchanger involves a problem such that it is difficult to enhance the heat transfer efficiency by decreasing the width of the louvers.
A heat exchanger that improves the above-noted problem is disclosed in U.S. Pat. No 2,789,797 which shows a structure wherein louvers are severed and raised in an alternate manner in a direction of air flow to form louver units, and heights of the louvers are changed between the adjacent louvers spaced in the direction of the air flow by a distance corresponding to a length of each louver. However, in the heat exchanger disclosed in U.S. Pat. No. 2,789,797, some adjacent louvers are spaced only by approximately one fourth of the fin pitch, and hence, it would be difficult to separate the temperature boundary layers along such louvers. At the same time, water droplets or dust would be adhere to such louvers, to prevent the air from flowing smoothly and to reduce the heat transfer performance. Also, because of the prevention of the air flow, the flow resistance would be increased. Thus, the prior art heat exchangers suffer from such problems.